Gene therapy approach to FAP: in vivo influence of T119M in TTR deposition in a transgenic V30M mouse model

Adeno-associated virus-9 reverses delayed gastric emptying of solids in diabetic mice

BACKGROUND

Gastroparesis is defined by delayed gastric emptying (GE) without obstruction. Studies suggest targeting heme oxygenase-1 (HO1) may ameliorate diabetic gastroparesis. Upregulation of HO1 expression via interleukin-10 (IL-10) in the gastric muscularis propria is associated with reversal of delayed GE in diabetic NOD mice. IL-10 activates the M2 cytoprotective phenotype of macrophages and induces expression of HO1 protein. Here, we assess delivery of HO1 by recombinant adeno-associated viruses (AAVs) in diabetic mice with delayed GE.

METHODS

C57BL6 diabetic delayed GE mice were injected with 1 × 1012 vg scAAV9-cre, scAAV9-GFP, or scAAV9-HO1 particles. Changes to GE were assessed weekly utilizing our [13 C]-octanoic acid breath test. Stomach tissue was collected to assess the effect of scAAV9 treatment on Kit, NOS1, and HO1 expression.

KEY RESULTS

Delayed GE returned to normal within 2 weeks of treatment in 7/12 mice receiving scAAV9-cre and in 4/5 mice that received the scAAV9-GFP, whereas mice that received scAAV9-HO1 did not respond in the same manner and had GE that took significantly longer to return to normal (6/7 mice at 4-6 weeks). Kit, NOS1, and HO1 protein expression in scAAV9-GFP-treated mice with normal GE were not significantly different compared with diabetic mice with delayed GE.

CONCLUSIONS AND INFERENCES

Injection of scAAV9 into diabetic C57BL6 mice produced a biological response that resulted in acceleration of GE independently of the cargo delivered by the AAV9 vector. Further research is needed to determine whether use of AAV mediated gene transduction in the gastric muscularis propria is beneficial and warranted.

Structure restoration and aggregate inhibition of V30M mutant transthyretin protein by potential quinoline molecules

Transthyretin (TTR) is a tetrameric protein found in human plasma and cerebrospinal fluid that functions as a transporter of thyroxine (T4) and retinol. A mutation resulting in the substitution of valine to methionine at position 30 (V30M) is the most common mutation that destabilizes the tetramer structure of TTR protein resulting in a fatal neuropathy known as TTR amyloidosis. The V30M TTR-induced neuropathy can be inhibited through stabilization of the TTR tetramer by the binding of small molecules. We accessed the potential of in-house synthesized quinoline molecules to stabilize the V30M TTR structure and analyzed the impact of protein-ligand interactions through molecular docking, molecular dynamics (MD) simulations, steered MD, and umbrella sampling simulations. This study revealed that the binding of quinoline molecules reverted back the structural changes including the residual flexibility, changes in secondary structural elements, and also restored the alterations in the electrostatic surface potential induced by the V30M mutation. Further, the top-most 4G and 4R molecules were compared with an FDA-approved drug (Tafamidis) and a reference quinoline molecule 14C. Here, we intend to suggest that the quinoline molecules could revert the structural changes, cease tetramer dissociation, prevent abnormal oligomerization and therefore could be developed as an effective therapeutics against TTR amyloidosis.

Hereditary Transthyretin-Related Amyloidosis: Genetic Heterogeneity and Early Personalized Gene Therapy

Point mutations of the transthyretin (TTR) gene are related with hereditary amyloidosis (hATTR). The number of people affected by this rare disease is only partially estimated. The real impact of somatic mosaicism and other genetic factors on expressivity, complexity, progression, and transmission of the disease should be better investigated. The relevance of this rare disease is increasing and many efforts have been made to improve the time to diagnosis and to estimate the real number of cases in endemic and non-endemic areas. In this context, somatic mosaicism should be better investigated to explain the complexity of the heterogeneity of the hATTR clinical features, to better estimate the number of new cases, and to focus on early and personalized gene therapy. Gene therapy can potentially improve the living conditions of affected individuals and is one of the central goals in research on amyloidosis related to the TTR gene, with the advantage of overcoming liver transplantation as the sole treatment for hATTR disease.

Biophysical characterization and modulation of Transthyretin Ala97Ser

Objective

Ala97Ser (A97S) is the major transthyretin (TTR) mutation in Taiwanese patients of familial amyloid polyneuropathy (FAP), characterized by a late‐onset but rapidly deteriorated neuropathy. Tafamidis can restore the stability of some mutant TTR tetramers and slow down the progression of TTR‐FAP. However, there is little understanding of the biophysical features of A97S‐TTR mutant and the pharmacological modulation effect of tafamidis on it. This study aims to delineate the biophysical characteristics of A97S‐TTR and the pharmacological modulation effect of tafamidis on this mutant.

Method

The stability of TTR tetramers was assessed by urea denaturation and differential scanning calorimetry. Isothermal titration calorimetry (ITC) was used to measure the binding constant of tafamidis to TTR. Nuclear magnetic resonance spectroscopy (NMR) titration experiment was used to map out the tafamidis binding site.

Results

Chemical and thermal denaturation confirmed the destabilization effect of A97S. Consistent with other the amyloidogenic mutant, A97S‐TTR has slightly lower conformational stability. NMR revealed the binding site of A97S‐TTR with tafamidis is at the thyroxine binding pocket. The ITC experiments documented the high affinity of the binding which can effectively stabilize the A97S‐TTR tetramer.

Interpretation

This study confirmed the structural modulation effect of tafamidis on A97S‐TTR and implied the potential therapeutic benefit of tafamidis for A97S TTR‐FAP. This approach can be applied to investigate the modulation effect of tafamidis on other rare TTR variants and help to make individualized choices of available treatments for FAP patients.

Emerging therapeutic targets currently under investigation for the treatment of systemic amyloidosis

INTRODUCTION

Systemic amyloidosis occurs when one of a growing list of circulating proteins acquires an abnormal fold, aggregates and gives rise to extracellular amyloid deposits in different body sites, leading to organ dysfunction and eventually death. Current approaches are mainly aimed at lowering the supply of the amyloidogenic precursor or at stabilizing it in a non-amyloidogenic state, thus interfering with the initial phases of amyloid formation and toxicity. Areas covered: Improved understanding of the pathophysiology is indicating novel steps and molecules that could be therapeutically targeted. Here, we will review emerging molecular targets and therapeutic approaches against the main forms of systemic amyloidosis at the early preclinical level. Expert opinion: Conspicuous efforts in drug design and drug discovery have provided an unprecedented list of potential new drugs or therapeutic strategies, from gene-based therapies to small molecules and peptides, from novel monoclonal antibodies to engineered cell-based therapies. The challenge will now be to validate and optimize the most promising candidates, cross the bridge from the preclinical phase to the clinics and identify, through innovative trials design, the safest and most effective combination therapies, striving for a better care, possibly a definitive cure for these diseases.

Tissue remodeling after interference RNA mediated knockdown of transthyretin in a familial amyloidotic polyneuropathy mouse model

Transthyretin (TTR) deposition in the peripheral nervous system is the hallmark of familial amyloidotic polyneuropathy (FAP). Currently, liver transplantation is the only available treatment to halt the progression of clinical symptoms; however, due to the limitations of this procedure, development of alternative therapeutic strategies is of utmost importance. In this regard, interference RNA (RNAi) targeting TTR is currently in phase III clinical development. To dissect molecular changes occurring in dorsal root ganglia (DRG) upon RNAi-mediated knockdown of TTR, we treated both chronically and acutely an FAP mouse model, in different stages of disease. Our data show that inhibition of TTR expression by the liver with RNAi reverse TTR deposition in DRG, decrease matrix metalloproteinase-2 (MMP-2) protein levels in plasma, inhibit Mmp-2 gene expression and downregulate MMP-9 activity in DRG, indicating extracellular matrix remodeling. Furthermore, protein levels of MMP-2 were found upregulated in plasma samples from FAP patients indicating that MMP-2 might be a novel potential biomarker for FAP diagnosis. Collectively, our data show that silencing TTR liver synthesis in vivo can modulate TTR-induced pathology in the peripheral nervous system and highlight the potential of MMP-2 as a novel disease biomarker.

The transthyretin amyloidoses: advances in therapy

There are two forms of transthyretin (TTR) amyloidosis: non-hereditary and hereditary. The non-hereditary form (ATTRwt) is caused by native or wild-type TTR and was previously referred to as senile systemic amyloidosis. The hereditary form (ATTRm) is caused by variant TTR which results from a genetic mutation of TTR. The predominant effect of ATTRwt amyloidosis is on the heart, with patients having a greater left ventricular wall thickness at presentation than the devastating form which is light chain (AL) amyloidosis. ATTRm amyloidosis is broadly split into two categories: a type that predominantly affects the nervous system (often called familial amyloid polyneuropathy (FAP)) and one with a predilection for the heart (often called familial amyloid cardiomyopathy (FAC)). Approximately half of all TTR mutations known to express a clinical phenotype cause a cardiomyopathy. Since the introduction of orthotopic liver transplantation for ATTRm amyloidosis in 1991, several additional therapies have been developed. These therapies aim to provide a reduction or elimination of TTR from the plasma (through genetic approaches), stabilisation of the TTR molecule (to prevent deposition) and dissolution of the amyloid matrix. We describe the latest developments in these approaches to management, many of which are also applicable to wild-type amyloidosis.

Recombinant adeno-associated virus vectors in the treatment of rare diseases

INTRODUCTION

An estimated 25 million Americans are living with rare diseases. Adeno-associated virus (AAV)-mediated gene therapy is an emerging therapeutic option for the more than 7,000 identified rare diseases. This paper highlights the benefits of AAV therapy compared to conventional small molecules, discusses current pre-clinical and clinical applications of AAV-mediated gene therapy, and offers insights into cutting edge research that will shape the future of AAV for broad therapeutic use.

AREAS COVERED

In this review the biology of AAV and our ability to generate disease-specific variants is summarized. Limitations of current therapy are reviewed, with an emphasis on immune detection of virus, viral tropism and tissue targeting, and limitations of gene expression. Information for this review was found using PubMed and clinicaltrials.gov.

EXPERT OPINION

Currently the scope of clinical trials of AAV gene therapy is concentrated in an array of phase I/II safety trials with less than two dozen rare diseases featured. Pre-clinical, translational studies are expanding in number as developments within the last decade have made generation of improved AAV vectors available to more researchers. Further, one bottleneck that is being overcome is the availability of disease models, which will allow for improved preclinical testing and advancement of AAV to more clinical applications.